This invention relates to magnetic recording methods and magnetic recording heads, and, in particular, to improvements where two information signals are recorded in such a manner as to overlay or overlap one another on the recording media The first track and the second track cross each other without generating crosstalk during reproduction of the two lines of information.
Various technical improvements have been proposed in order to increase the recording density on magnetic recording media when information is magnetically recorded. According to one of these methods for increasing the density, the width of the track on which information is recorded is made narrower However narrowing the track width results in frequent off-tracking of the magnetic head during reproduction even though a servomechanism is used to sustain the correct tracking In order to solve this problem, it has been proposed to interpose a guard band, having no magnetic information thereon, between adjacent tracks. It is apparent that this guard band is an idle or waste portion of the information recording medium. Recently, a so-called guard-bandless recording method has been proposed in which information is recorded on the guard band portion, as well as on the adjacent tracks, with different azimuth angles or mutually differing angles of azimuth. As a result, it is possible to prevent crosstalk between the adjacent tracks.
High density information recording has been attained, because the guardband-less recording method uses almost the whole surface of the magnetic recording medium in order to obtain effective recording of information. The information is recorded as a single layer on the magnetic recording medium in the guard-band-less recording method. It is apparent that the recording density could be increased if overlapping of overlaid tracks could be recorded on the magnetic recording medium. In such a multi-recording method, a plurality of information signals are recorded on a single track or the same portion of the magnetic recording medium in such a manner that no crosstalk is generated between the different signals during reproduction.
According to the prior art or the conventional video signal recording method, a color difference signal Sc of relatively low frequency and a brightness signal Sy of relatively high frequency are recorded on a single track of the magnetic recording medium by a single magnetic head. This is known as a multi-frequency recording method. In an electronic still camera system or a TV photo system, a video signal Sv consisting of a color difference signal Sc and a brightness signal Sy, respectively having the particular frequential allocations as shown in FIG. 1, is recorded on a floppy disc recording medium using a color difference line sequential FM recording system.
As mentioned above, in the prior art, the video signal is recorded on a single track by a single magnetic head by multi-frequency recording, and, as a result, cross modulation is generated between the color difference signal Sc and the brightness signal Sy. This disadvantageous phenomenon is generated when the information is reproduced, due to the non-linearity of the characteristics of the magnetic recording medium and the magnetic head being swept on the medium. That is when the color difference signal Sc and the brightness signal Sy have mutually different frequencies and are supplied to a circuit element having non-linear characteristics, mutual interference is created between the color difference signal and the brightness signal, resulting in the generation of a frequency component which has no relation to the video signal This frequency component causes noise during reproduction and the noise appears as ghost images on the screen.
In order to lessen cross modulation in the still camera system for magnetic recording and reproducing, various restrictions that differ according to the particular standard are provided. One example of these restrictions is that the recording current of the color difference signal Sc must be restrained or determined in such a manner that a spurious component of fy (=carrier frequency of brightness signal Sy=7 MHz)-2fc (=carrier frequency of color difference signal Sc=1.25 MHz) is made less than -33 dB relative to fy. Using the electronic camera system according to the prior art, the brightness signal Sy can be easily recorded with the most suitable recording current, however the color difference signal Sc must be recorded with a recording current which is considerably lower than the most suitable recording current. As a result, the signal level of the color difference signal obtained during reproduction of the information becomes low and color inversion is apt to happen on the screen.
In general, in the conventional techniques for multi-frequency recording of a color signal Sc and brightness signal Sy on a single track in the magnetic recording medium by means of a single head, when the value of the recording current of the color difference signal Bc is made as high as that of the most suitable recording current, cross modulation occurs, and when the color difference signal Sc is made so low that it agrees with the current standard of the electronic still camera system, color inversion is likely to be caused on the display. It is apparent that the picture quality deteriorates as a result of this phenomenon.
FIGS. 2(a). (b) depict a diagrammatical arrangement of magnetic domains and magnetic recording heads. The heads. 1 and 2, respectively have azimuth angles of approximately 45.degree. clockwise and counterclockwise relative to relative movement direction A. The recording medium 3 has magnetic domains and these domains are preferably arranged or directed at random. Of the magnetic domains shown in FIG. 2(a), some (3a) have their longitudinal axes parallel to a magnetizing direction B along which the gap of the magnetic head 1 advances, other domains (3b) have longitudinal axes which cross the magnetizing direction B at an angle of 45.degree., and still other domains (3c) cross the direction B at a right angle.
As clearly shown in FIG. 2(a). when the magnetic head 1 records information on the magnetic recording medium 3 the particular domains 3a are easily changed in their magnetic condition, other domains 3c are hardly changed in their magnetic condition, and the still other domains 3b change a little in their magnetic conditions. That is, when the magnetic head 1 sweeps along the recording medium 3 in the particular situation shown in FIG. 2(a). the information is recorded mainly on the magnetic domains 3a.
As a result, when a first information signal is recorded on the first track in the magnetic medium by the magnetic head 1 and then a second information signal is recorded by the second magnetic head 2 on the second track and is overlaid on the first one, the magnetic domains 3a mainly record the first information and coexist with other domains 3c having chiefly the second information with a negligible degree of interference. Thus, it is possible to record two kinds of information on a single track.
When the magnetic head 1 sweeps the track, formed as mentioned above, to reproduce the data mentioned above, the first information recorded in the magnetic domains 3a arranged parallel to the magnetizing direction is predominately read out, but a small amount of the second information which is recorded in the domains 3c so directed as to cross the magnetizing direction B at right angles is reproduced due to the azimuth loss of the domains 3c. The output level of the second information signal is less than that of the first information signal.
When magnetic head 2 shown in FIG. 2(b) sweeps along the magnetic recording medium 3, the second information signal recorded in the magnetic domains 3c arranged in parallel to the magnetizing direction C is predominately reproduced and the first information signal recorded in the domains 3a extending across the magnetizing direction C at right angles is reproduced to a degree which is smaller than that of the second information signal due to the azimuth loss of the domains 3a encountered during the reproducing process. In principle, two information signals recorded on the same track can be reproduced individually without any crosstalk between them.
In practice, the arrangement directions of the magnetic domains on the magnetic recording medium 3 cannot be simply categorized into three groups of domains as mentioned above. A group of magnetic domains has every arrangement direction, they are arranged completely at random, so that a small amount of crosstalk is generated during the reproducing process. However, it is possible to obtain an output having a practically small S/N value when the azimuth angle and recording current and the like are suitably selected.